A built in overflow is the most efficient method of draining aquarium water to a filter. If your aquarium does not have built-in overflow, CPR Continuous Siphon Overflows/Prefilters are the best means for getting water from an aquarium to a filter system without expensive modifications to the tank. They quietly skim up to six times more water than units with tubes. *NOTE* Air can get trapped in your overflow from time to time and will need bled out. You can avoid this by hooking up an AquaLifter Air Water Feed Pump or venturi pump, keeps it free of bubbles and always restarts perfect.
 
  The advantages of CPR Continuous Siphon Overflows/Prefilters include: 

* Adjustable water level allows you to 
  easily change the level in your tank. 
* Black top reduces algae growth. 
* Plastic screen to prevent fish loss. 
* Quiet operation.